package zijie;

import java.util.List;

public class addTwoNumbers_2_3 {

    public static void main(String[] args) {

    }

    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        ListNode head = null;
        ListNode tail = null;
        int carry = 0;
        while (l1 != null || l2 != null){
            int n1 = l1 != null ? l1.val : 0;
            int n2 = l2 != null ? l2.val : 0;

            int sum = n1 + n2 + carry;
            if(head == null){
                head = tail = new ListNode(sum % 10);
            }else{
                tail.next = new ListNode(sum % 10);
                tail = tail.next;
            }
            carry = sum/10;
            if(l1 != null){
                l1 = l1.next;
            }
            if(l2 != null){
                l2 = l2.next;
            }
        }
        if(carry > 0){
            tail.next = new ListNode(carry);
        }
        return head;



    }
    public ListNode addTwoNumbers2(ListNode l1, ListNode l2) {
       ListNode head = null;
       ListNode tail = null;
       int step = 0;
       while (l1 != null || l2!=null){
           int n1 = l1 != null ? l1.val : 0;
           int n2 = l2 != null ? l2.val : 0;
           int sum = n1 + n2 + step;
           int value = sum % 10;
           step = sum /10;
           if(head == null){
               head = tail = new ListNode(value);
           }else{
               tail.next = new ListNode(value);
               tail = tail.next;
           }
           if(l1 != null) {
               l1 = l1.next;
           }
           if (l2 != null) {
               l2 = l2.next;
           }

       }
       if(step > 0){
           tail.next = new ListNode(step);
       }
       return head;
    }
  public class ListNode {
      int val;
      ListNode next;
      ListNode() {}
      ListNode(int val) { this.val = val; }
      ListNode(int val, ListNode next) { this.val = val; this.next = next; }
  }

}
